Optical proximity and motion detector systems are used in a wide variety of applications, from robotic systems to security systems. The optical detectors in such systems detect large movements, which would not be suitable for use as an input interface to a computing system for receiving user input, for example. In some instances, such systems utilize a large number of optical sensors, which allows for pixel-level image processing to be used to detect motion of an object. Unfortunately, the large number of optical sensors increases the overall cost, and image processing consumes a large amount of power, making such systems unsuitable for use with computing systems, and particularly battery-powered or portable systems.
Conventionally, motion detectors can include single-mode detectors, active or passive, for motion detection. Active detectors can use multiple light-emitting diode (LED) sources to provide light to illuminate an object from at least three directions to triangulate a position of the object. Such systems can include reflectance-based proximity sensors and can use an associated algorithm configured to determine motion of the object by comparing changes in reflectance from the LED sources. Another conventional technique for active motion detection uses a discrete photo detector pair in connection with a focused reflected beam.
Passive motion detectors can be realized using a passive photo detector array configured to capture images and to detect motion through image processing. Unfortunately, image processing consumes too much power for use in portable computing systems. Another passive motion detector uses a pair of passive infrared detectors overlaid with a Fresnel lens, which gathers light and directs in onto the pair of passive infrared detectors. Unfortunately, such systems fail to provide sufficient resolution for use as an input device for a computing system.